flutter中TabBar和TabBarView保持状态方法

flutter使用TabBarView组件分页显示数据，来回切换页面，会触发页面的init和build，而且页面会回到最顶端，需要加个保持状态，方法共3步：

1.在每个页面都混入with AutomaticKeepAliveClientMixin

class MyViewPageState extends State<MyViewPage>
    with AutomaticKeepAliveClientMixin{
    }

2.在这些页面里重写wantKeepAlive方法，写法固定的

class MyViewPageState extends State<MyViewPage>
    with AutomaticKeepAliveClientMixin{
    @override
  // TODO: implement wantKeepAlive
  bool get wantKeepAlive => true;
    }

3.在这些页面的build开头调用super.build()

class MyViewPageState extends State<MyViewPage>
    with AutomaticKeepAliveClientMixin{
    @override
  // TODO: implement wantKeepAlive
  bool get wantKeepAlive => true;
  
 @override
  Widget build(BuildContext context) {
    super.build(context);
    return Container();
    }

再来切换tab，会发现这这页面init和build不会重复调用，并且原来滚动到底端的页面，切回来还是在底端。